![]() ![]() The distribution of ADF changed over early development from 50 % yolk sac, 42 % body surface and 8 % branchial in newly hatched fish to 68 % branchial and 32 % cutaneous at the end of yolk resorption. The total anatomical diffusion factor (ADF, mass-specific surface area per unit diffusion distance) remained constant over early development and appeared to be higher than in adult fish. ![]() Diffusion distances across both the filaments and lamellae of the gills decreased through development, from 3.7 to 2.4 µm for lamellae and from 14.5 to 10.8 µm for filaments. Harmonic mean diffusion distance across the skin increased through development from 20 µm at hatch (14 µm across the yolk sac) to 70 µm in an 11 g fish. ![]() The branchial contribution to total area increased rapidly, however, so that by the end of yolk absorption (body mass 0.190.23 g) it constituted 22 % of the total area and overtook cutaneous surface area between 5 and 6 g wet body mass. Cutaneous surfaces accounted for over 95 % of the total area available for respiration in newly hatched Atlantic salmon (body mass 0.0320.060 g). Newly hatched Atlantic salmon have poorly developed gills but do have a high skin area to mass ratio and a large well-vascularized yolk sac. During development from larva to juvenile in Atlantic salmon, Salmo salar, there is a change in the anatomical potential for gas exchange among gills, body skin and yolk sac as the larvae resorb yolk, grow and develop gills. ![]()
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